1. Field of the Invention
The present invention relates generally to fuel control for internal combustion engines and, more particularly, to a method of determining start of closed-loop fuel control for an internal combustion engine in an automotive vehicle.
2. Description of the Related Art
Typically, automotive vehicles include internal combustion engines having fuel control in accordance with engine control strategies. Many current engines operate without closed-loop fuel control for a variable amount of time after engine starting. For example, current engine control strategies rely on timers to delay operation of fuel control after engine starting to allow for sensor/component preconditioning. This time delay allows an oxygen (O.sub.2) sensor time to heat up and reach an active state before it can operate reliably to aid in controlling fuel and air to the engine. Minimizing this time delay (within limits of system functionality) generally improves engine control and reduces exhaust emissions from the engine.
Generally, the time to reach an active state for the oxygen sensor varies based on what the vehicle does after engine start. If the vehicle sits at idle, relatively cool exhaust gases blow across the oxygen sensor and tend to cool it. If the vehicle is driven away, the exhaust gases are much hotter and will not cool but may even tend to heat the oxygen sensor. Since current engine control strategies allow a fixed time delay value to be chosen for the closed-loop fuel control transition, it must be calibrated for the worst case idle only condition. This time delay value could be better modeled and minimized by using a measurement of energy input to the engine. As a result, there is a need in the art to minimize the time delay before beginning closed-loop fuel control for the engine that is uniquely adapted to the actual operating conditions after each engine start.